1) Field
Embodiments of the present invention pertain to the field of semiconductor processing and, in particular, to methods of dicing semiconductor wafers, each wafer having a plurality of integrated circuits thereon.
2) Description of Related Art
In semiconductor wafer processing, integrated circuits are formed on a wafer (also referred to as a substrate) composed of silicon or other semiconductor material. In general, layers of various materials which are either semiconducting, conducting or insulating are utilized to form the integrated circuits. These materials are doped, deposited and etched using various well-known processes to form integrated circuits. Each wafer is processed to form a large number of individual regions containing integrated circuits known as dice or dies. Each die may have metal bumps and/or pads for electrical coupling to other dies or boards (e.g., printed circuit boards (PCBs)). Typically, a “bump” refers to a soldering point on a front side of a device, and a “pad” refers to a soldering point on a back side of a device. In three dimensional (3D) packaging, the bumps on one die may be solder-bonded to the pads on another die. For example, the bumps of a die are bonded to pads of a PCB.
Metal alloys such as Tin alloys (e.g., SnAg) are widely used for metal bumps and pads in die packaging applications. The surface condition of these bumps or pads can directly affect bonding processes such as thermal compression bonding. One typical issue is that during bump and pad formation and subsequent processes prior to bonding, the bumps and pads may become easily oxidized. The oxidization layer can adversely affect the bonding process. Typically, flux is used to remove the oxidization layer on the bumps and pads, however, processes using flux typically require the application of heat onto the bumps to facilitate the oxidization layer removal. Too much heat can negatively affect die quality, particularly in 3D packaging applications where multiple dies are stacked together. The accumulated heat input can weaken the dies both electronically and mechanically. Other methods for bump or pad cleaning have been explored, but have drawbacks including high cost, and the risk of subsequent oxidation after cleaning.
Furthermore, using a soldering flux to remove an oxidation layer from the bumps and pads prior to bonding can result in a flux residue left on the bumps and pads. Cleaning the flux residue is difficult, especially in dies including dense through-silicon vias. Because of the difficulties involved in removing flux residue, existing manufacturing methods leave the flux residue on the ICs, resulting in erosion of the metal bumps or pads over time, which can reduce the long term reliability of the packages.